1. Field of the Invention
The present invention relates to an EL (electro-luminescence) display device fabricated by forming a semiconductor device (a device utilizing a semiconductor thin film; typically a thin film transistor) onto a substrate. The present invention further relates to an electrical equipment including such an EL display device as a display section.
2. Description of the Related Art
Recently, a technique for forming a thin film transistor (hereinafter referred to as TFT) onto a substrate has significantly advanced, and its application to an active-matrix display device has been developed. In particular, the TFT employing a polysilicon film therein has a field effect mobility higher than that of the conventional TFT employing an amorphous silicon film, and therefore, can operate at higher speed. Thus, a control function for pixels, that is conventionally performed by an external driver circuit provided at the outside of the substrate, can be performed by a driver circuit that is provided on the same substrate as the pixels.
The active-matrix display device as mentioned above can provide various advantages such as reduction in the manufacturing cost, downsizing of the display device, improvement of the yield, reduction in the throughput or the like, when various circuits and/or devices are fabricated on one and the same substrate. Thus, this kind of active-matrix display device has drawn much attention.
In an active-matrix EL display device, a switching device employing a TFT (hereinafter referred to as switching TFT) is provided at each pixel, and each of the respective switching TFTs allows a corresponding drive device for controlling current (hereinafter referred to as current-controlling TFT) to drive, thereby causing an EL layer (more strictly speaking, a light emitting layer) to emit light. An exemplary EL display device is described, for example, in Japanese Patent Application Laid-Open No. Hei. 10-189252.
The EL display device includes a device section composed of a cathode, an EL layer, and an anode (hereinafter, the device composed of these portions is referred to as EL device). When a film resistance of the anode in the device section increases, the in-plane distribution of electrical potentials in the anode becomes non-uniform due to the voltage drop, thereby resulting in disadvantages such as deviations in the light intensity of the EL device.